Solvent bonding of synthetic fibers

ABSTRACT

SYNTHETIC FIBERS ARE BONDED TOGETHER THROUGH TREATMENT WITH A MULTICOMPONENT LIQUID UPON INITIAL CONTACT WITH THE FIBERS IS A NON-SOLVENT THEREFOR BUT WHICH UPON EVAPORATION OF ONE OF THE COMPONENT BECOMES A FIBER SOLVENT.

United States Patent US. Cl. 8-1301 1 Claim ABSTRACT OF THE DISCLOSURE Synthetic fibers are bonded together through treatment with a multicomponent liquid which upon initial contact with the fibers is a non-solvent therefor but which upon evaporation of one of the component becomes a fiber solvent.

This application is a continuation of US. application Ser. No. 292,113, filed July 1, 1963, now abandoned.

The present invention relates to improved means for bonding fibers together, especially as non-woven fabrics, and, more particularly, to the discovery of new bonding agents which improve the quality of the fiber-fiber bond formed.

Nonwoven fabrics have been known for long periods of time, and are manufactured by bonding fibers together directly, without first spinning them as a yarn and weaving or knitting the yarn. A variety of such nonwoven fabrics are known, ranging from light-weight paper type materials to heavier products which resemble cloth. In all cases, some form of treating agent is applied to the fibers which bonds them together at points where they intersect. Similarly, 'woven and knitted fabrics may be subjected to these treating agents to lock the yarns together.

One well-known bonding technique uses a resin as a bonding agent. The resin is applied as a fluid which can stiffen or set and act as a sort of permanent adhesive for holding the fibers or yarns together. Another technique employs a treating agent which softens the fibers themselves so that they become tacky and bond together. Then the treating agent is removed or deactivated; the fibers lose their tackiness but remain firmly bonded.

In this latter procedure, one of the more common types of treating agent is a two-component liquid solution, of which one component is substantially more volatile than the other. The proportions of the components are selected so that the fibers are not soluble in the initial solution but are soluble after a proportion of the more volatile component evaporates and then insoluble after all of it is driven off. These liquids are known as latent solvents because of their delayed action in softening the fibers.

An example of the latter technique is based upon the fact that nylon is softened by concentrated aqueous solutions of zinc chloride, but not by the dilute solutions. In a typical process, a web of nylon fibers is moistened with a dilute aqueous solution of zinc chloride, followed by removal of excess solution. Through capillary action, a small amount of solution remains at points where the fibers intersect. A heating step follows in which some of the water evaporates and the concentration of zinc chloride in the water remaining on the fibers increases. When the concentration increases sufliciently, the solution tends to dissolve and soften the nylon making it tacky, and the nylon fibers adhere to eachv other. Then, as the remaining water evaporates, the nylon is precipitated and hardened to its original state. However, the fibers which have been joined together when the nylon was tacky remain firmly bonded together. Similar procedures may be employed in knitted and woven nylon fabrics.

A need has existed for improved latent solvents to be use with synthetic fibers such as acetate rayon, polyesters,

modacrylic and nylon which would provide fabrics having improved launderability and resistance to chlorine bleach in laundering, increased strength and resistance to pilling, lumping and shrinkage. Accordingly, it is a principal object of the present invention to provide a process for bonding fibers to each other using novel latent solvents which are capable of forming, in synthetic fibers, very strong fiber-fiber bonds to produce fabrics that are superior in all respects. Other objects will be apparent from the following detailed description of the invention.

In practicing the invention, the latent solvent comprises one or more of the organic compounds described herein, dissolved emulsified and dispersed in water or another suitable liquid. This latent solvent is applied to a knitted or woven fabric or a nonwoven fabric web. Excess liquid may be removed and then the fabric is dried, preferably at an elevated temperature.

The new latent solvents comprise solutions, emulsions or dispersions of at least one of the following compounds. When it is used in solution, the compound should be selected to be sufficiently soluble in water or a mixture of water with a water-miscible organic solvent to give a 1% solution and preferably up to 10% solution at room temperature (2025 (3.). However, compounds which are not soluble in water alone may be employed in emulsion or dispersion in water. This avoids the cost and hazard of using ordinary water-miscible organic solvents which may be toxic or flammable.

The compounds useful for the present invention include the following, the third group below being particularly preferred.

(1) Hydroxyaliphatic acids, particularly a-hydroxy lower saturated aliphatic monocarboxylic acids having up to about 6 carbon atoms.

(2) Aliphatic and aromatic polycarboxylic acids, particularly saturated aliphatic dicarboxylic acids such as w-alkylene-dicarboxylic acids having about 2 to 10 carbon atoms and monocyclic aromatic dicarboxylic acids.

(3) Substituted and unsubsituted polyhydroxy phenols, particularly the monocyclic and non-fused ring bicyclic phenols containing two or more hydroxyl groups. The substituted phenols which may be used include benzoic. acids substituted with at least two hydroxyl groups and polyhydroxy phenols carrying higher and lower alkyl groups. In compounds having more than one benzene ring, the hydroxyl groups may be on the same or different rings.

(4) Monohydric monocyclic phenols substituted with higher alkyl groups and/or alkoxy groups. The higher alkyl groups may be branched or straight chained but have at least about 6 carbon atoms and preferably 8 to 9 carbon atoms. The alkoxy groups have, preferably, about 1 to 4 carbon atoms.

(5) Substituted and unsubstituted monoand polyhydric naphthols.

The compounds of groups 3 and 4 are adaptable to a large number of fabrics and for this reason are particularly preferred.

The foregoing groups of compounds are exemplified by the following: (1) lactic acid; (2) adipic acid and terephthalic acid; (3) 2,4-dihydroxybenzoic acid, 2,5-dihydrexybenzoic acid, 3,4,5-trihydroxybenzoic acid, 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), 1,4-dihydroxybenzene (hydroquinone), 1,2,3-trihydroxybenzene (pyrogallol), 1,3,5 trihydroxybenzene (phloroglucinol), 1,2,4 trihydroxybenzene (hydroxyhydroquinone), 3,5-dihydroxytoluene (orcinol), S-hydroxy- 2-hexylphenol (hexyl resorcinol), o,o-biphenol and 2,2- bis (p-hydroxyphenyl) propane (bisphenol A); (4) octylphenol, nonylphenol and m-ethoxyphenol; (5) wnaphthol and 3-naphthol.

These compounds are dissolved emulsified or dispersed, as described above, in volatile liquids such as Water, alcohols, preferably lower, water-soluble alcohols, e.g., ethyl alcohol, and mixtures of Water with water-soluble alcohols, the resulting solution emulsion or dispersion being the latent solvent. It will be appreciated that cost and safety factors lead to a preference for water.

Generally, the latent solvents, particularly those in which the compound is dissolved in the liquid, contain about 1 to 20% and sometimes more, preferably 340% of the compound. Of course, for any given latent solvent, the more dilute solutions require evaporation of more of the water or other more volatile constituent before the critical concentration for softening the fibers is reached. However, to a certain extent, the lower bonding tendencies of more dilute solutions may be compensated for by the use of larger amounts of latent solvent on the fibers.

In use, fabrics or batts of fibers are impregnated with the latent solvent to a pick-up of about 60 to 120%, and the fabrics are then dried, usually at an elevated temperature of at least 200 F., and preferably 250 to 350 F. Then the fabric may be subjected to any desired finishing operations. It is possible to control the nature of the final product by varying the treatments applied after a nonwoven web, and, in some cases, a fabric, is impregnated with a latent solvent. If a lofty product is desired, the web may be subjected to vacuum extraction of excess latent solvents after impregnation, followed by heating the web with a stream of heated air flowing through the structure. If a high density product is desired, the curing step may comprise heating the web under pressure.

The drying step in many cases not only leads to bonding but also to removal of the above compounds which are added to the volatile liquid as constituents of the latent solvent. The reason for this is not fully understood, but it is believed that the compounds possess sufiicient vapor pressure to volatilize under the heat conditions. In those cases in which water is present, a microscopic steam distillation may take place. However, this vaporization does not interfere with the bonding process. Furthermore, when the compound is not removed during bonding, the fabric may be washed under neutral to alkaline conditions to remove essentially all of the bonding agent.

The invention is applicable to a wide variety of synthetic fibrous materials which include: polyesters, by which is meant polymers having repeating ester linkages in the chains thereof such as polyethylene terephthalate; polyamides having repeating amide linkages in the chains thereof formed, e.g., by polymerization of dibasic acids and polyamines such as polyhexamethylene adipamide (nylon 66) and polycaprolactam (nylon -6); polyacrylonitriles and copolymers of acrylonitrile with, e.g., vinyl chloride available as Orlon, Acrilan and -Dynel; cellulose acetate; and polyvinyl alcohol. These fibers may be used alone or in blends with each other. It is also possible to use fibers which are not affected by the treatment, but these are limited to amounts which will not interfere with efiicient bonding. The ratio of nonbonding fibers to bonding fibers usually is in the range 2:1 to 1:2.

Compound Adipiclacld Tcrephthalic a 2,4dihydroxybenzoic acid 2,5dihydroxybenzoic acid 3,4,5-trihydroxybenzoic acid Octyl phenol Nonyl phenoL.

M-ethoxy phenol 1,2-dihydroxybenzene (catecho Alpha'naphthol Beta-naphthol- The fibers are preferably in the size range of 1-15 denier, but smaller and larger sizes may be used where necessary for a desired end product. Usually, the fiber length is /2 to 2 /2 inches or longer for dry carding, garneting, and air deposition methods of web formation. For liquid processing as in paper making, fibers less than /2 inch are preferred.

The weight of the fabric or non woven fiber web subjected to the process also may vary according to the use intended for the final product. However, for non-woven fabrics, the initial fibrous material will usually weigh 0.5- 64 oz. per square yard. The fabrics may also be woven or knit and :based upon spun staple or continuous filament yarns.

The following examples illustrate the invention.

EXAMPIJE I A web of polyethylene terephthalate polyester fiber of 6 denier and 2 inch staple weighing 4.0 ounces per square yard is saturated with a 3% aqueous resorcinol solution. The web supported on a wire mesh grid is then passed over a vacuum extraction slot to remove the excess saturant and leave about wet pickup. It is then dried in air at a temperature of 200 F. A bonded fabric of relatively low density is produced and is useful as an apparel interlining.

EXAMPLE II Example I is repeated except that the web is dried at a temperature of 300 F. to evaporate residual resorcinol leaving the bonded fabric essentially free of resorcinol. The fabric does not discolor in light and is useful as an apparel interlining. However, the fabric may be washed in an aqueous medium to remove any remaining resorcinol.

EXAMPLE HI A web of nylon 66 polyamide fiber of 6 denier and 2" staple, weighing 16 oz. per sq. yd., is saturated with a 5% solution of Bisphenol A [2,2-bis (p-hydroxyphenyl) propane] in a 2:1 water-ethanol mixture. The web supported on a wire mesh grid is padded over a vacuum extraction slot to remove the excess saturant and leave about 60% wet pickup. It is then dried by passing a stream of air heated to a temperature of 300 F. through the web. The bonded web is then washed by passing open width through a hot water pad at 180 F., squeezed and dried. A flexible bonded fabric is produced which has excellent wet strength. It is useful as a nonlumping mattress pad filler.

In additional tests, a number of latent solvents were prepared and applied to a series of nonwoven fabric webs of a variety of synthetic textile materials. The efiiciency of bonding was determined in each case and the fabrics were rated accordingly on a scale of 0-4, 4 representing a good bond, 3 a fair bond, 2 a light bond, 1 a very light bond and 0 no bond. The results are given in Table I. It will be seen that excellent bonding is achieved in most cases, generally superior to that achieved with conventional latent solvents.

TABLE I Fibers Polyamide Poly- PV ester alcohol mpaawawwwawmmwppmw rorooc-w-omoc tomoooooooo OHOONlhi RNNHOOQQOOOOC mwwmwwmwww-wawmwmmmm w-waa-awnuropwoooooooco cotcww-mwxorczoocooe-wcm Many of the compounds in the foregoing table are soluble in water and may be applied to textiles in aqueous solution. Several of the compounds are not sufficiently soluble in water for some purposes, but, in accordance with the invention, they may be used either in solution in mixtures of miscible solvents or in aqueous emulsion or dispersion.

Since only a small part of the surfaces of the fibers is affected by the above treatment, the invention produces improved bonded fiber structures, particularly non-woven fabrics, in which synthetic fibrous materials are bonded without substantial loss of fibrous character, molecular orientation, strength, resilience, denier or other inherent characteristics. It is possible to produce fibrous structures of many and varied types, including flat, dense, paperlike materials, bulky, less dense, fabric-like products, lofty, low density warmth retaining, felt-like sheet materials (e.g., interlining), lofty, low density, load bearing felt and batting-like materials (e.g., mattress pad filler, pillow filler, etc.). The products may also be fiber filled laminates (e.g., polyesterglass fiber laminates). Accordingly, it will be appreciated that while a number of specific examples have been given to illustrate the invention, 'various modifications may be made Without deviating from the spirit and intent thereof as defined in the claim.

We claim:

1. A method of bonding linear synthetic polyester fibers together which comprises applying thereto a latent solvent consisting of a solution, dispersion or emulsion of (1) 0,0'biphenol, 2,2'-p-(hydroxyphenyl) propane, 3,5-dihydroxytoluene or S-hydroxy-Z-hexylphenol and (2) water, a water soluble lower alkanol or an aqueous solution of a 6 lower alkanol wherein the concentration of the first component of said later solvent is insufficient to soften said fibers upon initial contact and thereafter evaporating the second component to concentrate said first component on the surface of said fibers to soften said and promote bonding therebetween.

References Cited UNITED STATES PATENTS 1,935,263 11/1933 Ellis.

2,341,423 2/1944 Catlin.

2,365,931 12/1944 Binger.

2,808,311 10/1957 Hare.

2,849,359 8/195-8 Smith.

2,852,833 9/1958 Mueller.

3,053,609 9/1962 Miller.

3,063,787 11/ 1962 Rynkiewicy et al.

FOREIGN REFERENCES 609,945 10/ 1948 Great Britain. 

